// written at: luckylarry.co.uk
// variables to take x number of readings and then average them
// to remove the jitter/noise from the SRF05 sonar readings

const int numOfReadings = 10;                   // number of readings to take/ items in the array
int readings[numOfReadings];                    // stores the distance readings in an array
int arrayIndex = 0;                             // arrayIndex of the current item in the array
int total = 0;                                  // stores the cumlative total
int averageDistance = 0;                        // stores the average value

// setup pins and variables for SRF05 sonar device

int echoPin = A0;                                // SRF05 echo pin (digital 2)
int initPin = A1;                                // SRF05 trigger pin (digital 3)
unsigned long pulseTime = 0;                    // stores the pulse in Micro Seconds
unsigned long distance = 0;                     // variable for storing the distance (cm)

// setup pins/values for LED

int redLEDPin = 9;                              // Red LED, connected to digital PWM pin 9
int redLEDValue = 0;                            // stores the value of brightness for the LED (0 = fully off, 255 = fully on)

//setup

void setup() {

  pinMode(redLEDPin, OUTPUT);                   // sets pin 9 as output
  pinMode(initPin, OUTPUT);                     // set init pin 3 as output
  pinMode(echoPin, INPUT);                      // set echo pin 2 as input

  // create array loop to iterate over every item in the array

  for (int thisReading = 0; thisReading < numOfReadings; thisReading++) {
readings[thisReading] = 0;
 }
// initialize the serial port, lets you view the
 // distances being pinged if connected to computer
     Serial.begin(9600);
 } 

// execute
void loop() {
digitalWrite(initPin, HIGH);                    // send 10 microsecond pulse
delayMicroseconds(10);                  // wait 10 microseconds before turning off
digitalWrite(initPin, LOW);                     // stop sending the pulse
pulseTime = pulseIn(echoPin, HIGH);             // Look for a return pulse, it should be high as the pulse goes low-high-low
distance = pulseTime/58;                        // Distance = pulse time / 58 to convert to cm.
 total= total - readings[arrayIndex];           // subtract the last distance
readings[arrayIndex] = distance;                // add distance reading to array
total= total + readings[arrayIndex];            // add the reading to the total
arrayIndex = arrayIndex + 1;                    // go to the next item in the array
// At the end of the array (10 items) then start again
if (arrayIndex >= numOfReadings)  {
    arrayIndex = 0;
  }

  averageDistance = total / numOfReadings;      // calculate the average distance

  // if the distance is less than 255cm then change the brightness of the LED

  if (averageDistance < 255) {
    redLEDValue = 255 - averageDistance;        // this means the smaller the distance the brighterthe LED.
  }

  analogWrite(redLEDPin, redLEDValue);          // Write current value to LED pins
  Serial.println(averageDistance, DEC);         // print out the average distance to the debugger
  delay(100);                                   // wait 100 milli seconds before looping again

}
